Electronic devices that sense and store manual writing are known in the art. For instance, back-lit liquid crystal display capture terminals are able to sense and store manually written signals using a touch sensitive screen and have utility in capturing electronic signatures, such as for recording credit card signatures. Further, computers including personal digital assistants (PDA) and other palm-sized computers use a stylus and a touch screen in combination with a handwriting recognition program to record the handwriting.
However, the use of such touch sensitive screens or palm sized computers is often economically unaffordable in many applications since the devices that include input screens may be expensive. For example, in a hospital where each doctor treats several patients and prepare notes or reports about patient symptoms and progress, having to provide each doctor with a laptop or a PDA would be expensive and provide a non-flexible and non-user friendly interface for gathering data. In some instances, a two-dimensional device that generates and electronically stores handwritten data, text, sketches, and drawings is needed. Known two-dimensional digital devices include an output, such as a pen, that writes on a medium (i.e., paper) and an input, such as a digital camera, that captures a digital image of the data left on the medium by the output.
The location of the digital camera and the pen in relation to the medium may be determined by calculating a location of the two-dimensional device in relation to the medium using a coordinate system printed on the medium. For instance, a dot-pattern, such as a 6×6 matrix of black dots, may be printed on the medium using a traditional CMYK color space or a K color space wherein (C) is cyan, (M) is magenta, (Y) is yellow, and (K) is black in the visible region of the spectrum, i.e., about 400-700 nm. In the visible region of the spectrum, the colors are visible to the naked eye and are visible colorants. As the pen of the two-dimensional device is placed on the medium, the camera moves over the visible dot-pattern printed on the medium, extracts the visible dot-pattern, and decodes the position of the two-dimensional device in relation to the medium. The position and movement of the two-dimensional device on the medium can, thus, be determined and electronically stored.
However, since the digital camera is scanning a visible dot-pattern printed on the media, the presence of the visible dot-pattern may distort the readability, the aesthetic appearance, the overall image quality and flexibility in the document design layout, thus, decreasing the value of the information contained within the printed document. Further, if the medium is a pre-printed form having existing text, lines or boxes of ink, the visible, existing ink on the medium may hinder the effectiveness of the digital camera from recording the position of the two-dimensional device on the medium.